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Year 11
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Higher

Electrolysis of aqueous solutions

I can describe the reactions of electrolysis of an aqueous solution, including the tests for identifying the products.

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New
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Year 11
OCR
Higher

Electrolysis of aqueous solutions

I can describe the reactions of electrolysis of an aqueous solution, including the tests for identifying the products.

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Lesson details

Key learning points

  1. Multiple types of positive ions are in competition at the negative electrode (cathode).
  2. Multiple types of negative ions are in competition at the positive electrode (anode).
  3. There are rules for which substances are discharged at the anode and cathode.
  4. The gases produced during electrolysis can be collected and tested.
  5. Hydrogen may be formed at the cathode

Keywords

  • Aqueous solution - formed when a substance is dissolved in water

  • Cathode - a negatively charged electrode, in an electrolysis cell, to which the anions are attracted

  • Anode - a positively charged electrode, in an electrolysis cell, to which the cations are attracted

  • Electrolyte - a liquid or solution that contains freely moving ions

Common misconception

Recognising the particles present in an aqueous solution is problematic. Understanding how an electric current flows through an electrolyte is confusing as ions, not electrons, are the charge carrier.

Ensure that students have a good understanding of key terms such as atom, ion, electron, solutions and reactivity before moving on to the electrolysis of aqueous solutions.

Provide opportunities for students to carry out the electrolysis of aqueous solution for themselves. Before doing the practical, ask them to predict what will be formed at each electrode.
Teacher tip

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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Starter quiz

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6 Questions

Q1.
What is an ion and how is it formed?
It is a charged particle formed by an atom gaining or losing proton.
It is a neutral particle formed by an atom gaining or losing electrons.
Correct answer: It is a charged particle formed by an atom gaining or losing electrons.
It is a neutral particle formed by an atom gaining or losing neutrons.
Q2.
What does the law of conservation of mass state?
Mass can be created and destroyed, allowing for new matter.
Mass is always lost in a chemical reaction, reducing reactants.
Correct answer: Mass is neither created nor destroyed in a chemical reaction.
Q3.
What is electrolysis and what is its purpose?
It is a method of mixing substances to form a solution.
Correct answer: It is a process that uses electric current to drive a chemical reaction.
It is a technique for measuring the mass of an element.
It is the flow of electrons in a circuit.
Q4.
What is an aqueous solution?
It is a solution in which a substance is dissolved in acid.
Correct answer: It is a solution in which a substance is dissolved in water.
It is a solution in which a substance is dissolved in alcohol.
It is a substance in its liquid state.
Q5.
What is the role of the anode in electrolysis?
It is the negatively charged electrode where reduction occurs.
Correct answer: It is the positively charged electrode where oxidation occurs.
It is where the electrolyte is added.
Q6.
What is the role of the cathode in electrolysis?
Correct answer: It is the negatively charged electrode where reduction occurs.
It is the positively charged electrode where oxidation occurs.
It is where the electrolyte is added.

Exit quiz

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6 Questions

Q1.
Which ions compete to be discharged at the cathode?
negative ions
neutral ions
Correct answer: positive ions
Q2.
Which ions compete to be discharged at the anode, and what determines their discharge?
only negative ions compete; the more abundant ion is discharged
positive and negative ions compete; the ion with the highest charge is discharge
Correct answer: negative ions compete; the one with the lower reactivity is discharged
positive ions compete; the ion with the lower charge is discharged
Q3.
What gas is commonly formed at the cathode during the electrolysis of sodium chloride solution, and why?
chlorine, because it is produced at the cathode
Correct answer: hydrogen, because sodium is more reactive than hydrogen
oxygen, because it is a common gas
nitrogen, because it is the most abundant in the atmosphere
Q4.
How can you test for the presence of hydrogen gas, and what is the expected result?
it relights a glowing splint
it turns lime water milky
a litmus test; the paper turns red then bleaches white
Correct answer: the squeaky pop test
Q5.
What determines whether hydrogen or a metal is produced at the cathode during electrolysis?
the concentration of the electrolyte
Correct answer: the reactivity of the metal compared to hydrogen
the temperature of the solution
Q6.
What is the expected result when litmus paper is exposed to chlorine gas, and why?
Correct answer: it bleaches it white because chlorine is a strong oxidising agent
there is no change because chlorine is inert
it turns blue because chlorine is alkaline
Correct answer: it turns red because chlorine is acidic